test: add E2E tests for homepage vehicle lookup flow

- enters plate and sees vehicle info with CTA button:
  types HDO732, verifies Peugeot 107 1.0, 2011, Gul, Bensin appear,
  verifies Fortsatt till brevet link has correct href
- shows not found for unknown plate (ZZZ999)
- CTA navigates to compose when authenticated:
  logs in as test@bilhalsning.se, performs lookup, clicks CTA,
  verifies redirect to /compose?plate=HDO732

frontend/e2e/vehicle-lookup.spec.ts

@@ -0,0 +1,51 @@
+import { test, expect } from '@playwright/test'
+
+test.describe('Vehicle lookup', () => {
+  test('enters plate and sees vehicle info with CTA button', async ({
+    page,
+  }) => {
+    await page.goto('/')
+
+    await page.getByPlaceholder('ABC 123').fill('HDO732')
+    await page.getByPlaceholder('ABC 123').press('Enter')
+
+    await expect(page.getByText(/Peugeot 107 1\.0/)).toBeVisible({
+      timeout: 15_000,
+    })
+    await expect(page.getByText('2011').first()).toBeVisible()
+    await expect(page.getByText(/Gul/)).toBeVisible()
+    await expect(page.getByText(/Bensin/)).toBeVisible()
+
+    const cta = page.getByRole('link', { name: 'Fortsätt till brevet' })
+    await expect(cta).toBeVisible()
+    await expect(cta).toHaveAttribute('href', '/compose?plate=HDO732')
+  })
+
+  test('shows not found for unknown plate', async ({ page }) => {
+    await page.goto('/')
+
+    await page.getByPlaceholder('ABC 123').fill('ZZZ999')
+    await page.getByPlaceholder('ABC 123').press('Enter')
+
+    await expect(
+      page.getByText('Inget fordon hittades'),
+    ).toBeVisible({ timeout: 15_000 })
+  })
+
+  test('CTA navigates to compose when authenticated', async ({ page }) => {
+    await page.goto('/logga-in')
+    await page.getByLabel('E-postadress').fill('test@bilhalsning.se')
+    await page.getByLabel('Lösenord').fill('test1234')
+    await page.getByRole('button', { name: 'Logga in' }).click()
+    await page.waitForURL('/')
+
+    await page.getByPlaceholder('ABC 123').fill('HDO732')
+    await page.getByPlaceholder('ABC 123').press('Enter')
+
+    const cta = page.getByRole('link', { name: 'Fortsätt till brevet' })
+    await expect(cta).toBeVisible({ timeout: 15_000 })
+    await cta.click()
+
+    await expect(page).toHaveURL('/compose?plate=HDO732')
+  })
+})